We are sequencing the major histocompatability complex (MHC) class I peptides from Trypanosoma cruzi-infected cells. T. cruzi, a protozoan parasite carried by the reduviid bug, is the cause of a debilitating chronic heart disease in South America known as Chagas disease. Unfortunately, this disease cannot be treated except by using harmful chemotherapy. When a human cell encounters a protein, such as the foreign protein secreted by an invading parasite, it presents proteolytic peptide fragments on the surface of the cell associated with the MHC protein. By purifying these peptides using immuno-affinity chromatography, a battery of currently available HPLC techniques, and the gas-phase separation techniques available to us in mass spectrometry, we hope to be able to identify and sequence infection-specific MHC class I peptides so that a vaccine harnessing T-cell-mediated immunology can be developed to fight this fatal disease.